Warning Issued for Cancer Drug Avastin

Aug. 13, 2004 -- The recently approved cancer drug Avastin may
increase the risk of serious and potentially deadly blood clots in up to 5% of
people who use it, according to a drug warning issued today.

The drug's manufacturer, Genentech, Inc., and the FDA sent a
letter warning health care providers with new information about the potential
side effect yesterday. Avastin was approved in February for the treatment of
advanced colorectal cancer that has spread to other parts of the body.

In the letter, Genentech officials say there is evidence of an
increased risk of developing clots within blood vessels and arteries that could
become dislodged and travel to the heart or brain and lead to serious
complications, such as stroke or heart attack, associated with the use of
Avastin.

People who experience blood clots during treatment are advised
to stop taking the drug.

Avastin Linked to Blood Clots

In randomized clinical trials with advanced colorectal cancer
patients, the risk of serious blood clot-related events was nearly twice as
high in patients receiving Avastin in addition to standard chemotherapy vs.
those receiving chemotherapy alone. The estimated overall rate of these adverse
events was up to 5%.

The risk of these side effects was higher in people with a
prior history of blood clots in the arteries and those over age 65.

Genentech says it is currently developing revised labeling
information for the drug to include details on these risks. Genentech is a
WebMD sponsor.

Avastin is the first of a new class of drugs known as
angiogenesis inhibitors to be approved by the FDA. The drugs work by preventing
the formation of new blood vessels, a key factor in preventing the spread of
cancer as well other diseases.

Avastin is given by injection. The antibodies target a protein
called vascular endothelial growth factor (VEGF) that plays a role in making
new blood vessels for tumors (a process called angiogenesis). When Avastin
binds to the protein, it stops the growth of new blood vessels, which
eventually starves the tumor of the blood, oxygen, and other elements needed
for growth.